Fig. 1.

Saturated trivariate model depicting relationship between major depression, regular tobacco use and nicotine dependence. In this modified version of the causal–contingent–common pathway (CCC) model, the regression path (β) demonstrates that a score on the nicotine dependence scale is contingent on regular tobacco use. A, C and E represent latent additive genetic, common environmental and unique environmental sources of variance influencing the observed traits.